Waxy distillates and raffinates containing appreciable quantities of wax e.g. 30% or more wax are not easily dewaxed using conventional dewaxing techniques such as solvent dewaxing. High wax contents leads to an overload in solvent handling and recovery systems. Neither are such waxy feeds amenable to catalytic dewaxing because catalytic dewaxing converts the wax to low boiling products (i.e. light gases or light liquids boiling in the fuels range) which inevitably results in a reduction of lube oil yield Typically, therefore, the waxy feeds containing 30% or more wax are converted to fuels by a process of fractionation under atmospheric and vacuum distillation condition with the vacuum distillate being sent to a catalytic cracker. For a waxy oil to be considered a viable lube feed the wax content usually should be about 30% or less, preferably below 25%.
Waxy oils have been subjected in the past to hydrotreating followed by isomerization.
U.S. Pat. No. 3,487,005 teaches the production of low pour point lubricating oils, without recourse to physical wax separation, from a high pour point, non-asphaltic waxy oil containing organic nitrogen and sulfur compounds and boiling mostly above 800.degree. F. The process comprises first subjecting the waxy oil to catalytic hydrocracking-denitrification under specified conditions, to remove nitrogen and sulfur containing species from the oil and convert at least 20% of the feed into products boiling lower than the feed, and then subjecting at least the higher boiling components to catalytic isomerization-hydrocracking under specified conditions in the presence of an unsulfided naphtha reforming catalyst having no more than moderate acidity, and finally recovering from the isomerized product an 800.degree. F.+bottoms fraction having a pour point at least 30.degree. F. below the pour point of the waxy oil feed. In the isomerization-hydrocracking zone, at least 10% of the sweetened feed is converted to lower boiling materials.
The oil feeds used are preferably a straight run vacuum gas oil and deasphalted residual oils.
In the hydrocracking-denitrification zone, the conditions used are such that at least about 20% conversion of the feed to distillates lower boiling than the feed is achieved so as to obtain a high overall pour point reduction and to improve the viscosity index of the final product. Conditions in that first zone include temperature of 650.degree. to 900.degree. F., pressure of at least about 1000 psig hydrogen gas rate of at least 1000 SCF H.sub.2 /bbl and LHSV of 0.2 to 10. While some pour point reduction occurs in the first zone, it is not enough to significantly reduce the pour point of the highest boiling components unless conversion or treatment is carried far beyond what is needed to remove sulfur and nitrogen and thereby reduce product yield. The effluent from this first zone is passed to the isomerization zone. The isomerization zone is maintained at a temperature in the range of 700.degree. to 900.degree. F., pressure of 500 to 5000 psig, hydrogen gas rate of 2000 to 20,000 SCF H.sub.2 /bbl and LHSV of 0.2 to 10, conditions such that at least 10 wt % of the oil feed into zone 2 is hydrocracked to lower boiling distillates. The catalyst of zone 2 is a naphtha reforming catalyst, preferably a noble metal (i.e. Pt or Pd) on a porous refractory oxide such as alumina. The catalyst is of moderate acidity. This is achieved by promoting the alumina with a small amount of fluorine, 2 wt % or less. In an example, a catalyst containing 0.7 wt % Pt and 0.7 wt % fluorine on alumina is used to isomerize a hydrotreated straight-run gas oil distillate (Example 3).
U.S. Pat. No. 3,494,854 is directed at two stage catalytic hydrogen processing of a lube oil. A heavy lube oil distillate is converted into a refined mineral lube oil of reduced pour point. The raw waxy oil is contacted in a first zone with hydrogen in the presence of a sulfur-resistant HDS/HDN catalyst under hydrotreating conditions. The hydrotreated oil, after removal of low boiling components, is contacted in a second zone with hydrogen in the presence of a platinum group metal containing isomerization-hydrocracking catalyst containing a major amount of a calcium-exchanged crystalline alumino-silicate having pores of about 8 to 14 .ANG. and a silica to alumina mole ratio of about 2 to 3:1 and a minor catalytic amount of about 0.1 to 5 wt % of a platinum group metal. See also G.B. No. 1,381,004, U.S. Pat. No. 3,629,096, and U.S. Pat. No. 4,518,485.